It would be interesting to know how the shop arrived at $180.00 for labour. Was it two hours at $90.00, four at $45.00? Seems to me that either the hourly rate is quite high (may depend on your location, though) or that it took an inordinate amount of time to complete the work. It may have been some flat rate or some rate prescribed by some manual as used in car repairs. Anyway, not calling you with a quote is not very ethical/honest, but that appears to be par for the course these days. Like the other man said, the only pratical thing you can do is move on. I am curious as to the hum, one would think that they would have told you exactly what is causing it and what can be done to fix it, especially if they are so proud of their association with Mac. If it provides any form of relief, you can thank your lucky star you did not have to ship the unit across country or, worse yet, from Canada to the States, for repairs.
